This invention relates generally to tissue markings that are normally permanent, but can be erased that is, rendered colorless when desired. In particular, this invention relates to tissue marking, which can become colorless when infrared radiation is applied as well as to methods of their use.
Tattoos, which are a form of tissue markings, have been in use for thousands of years by many cultures for many purposes including artistry, beauty, identification, and religious purposes. Today the majority of tattoos are used for artistic expression as well as cosmetic applications such as permanent lip coloration, eyebrow coloration and eyeliner. Other uses for tattoos include corrective pigmentation following surgery and identification markings on animals.
The tattooing procedure consists of piercing the skin with needles or similar instruments to introduce an ink that typically includes particles of pigment suspended in a liquid carrier. Pigment particles that do not enter the dermis (larger pigment particles) and remain in the epidermis are sloughed off over time, whereas enough of the particles (smaller particles) that get lodged in the dermis are phagocytosed by dermal cells or retained in the extracellular matrix to create permanent markings. It should be noted that some of the ink particles in the dermis, particularly the minute particles may potentially be removed and/or relocated by the body's biological processes. Thus, a permanent tattoo is created when a sufficient number of pigment particles introduced into the body are retained in the dermis. Typical tattoo pigments include carbon black, inorganic metal salts and colored organometallic complexes.
Tattoos or tissue marking ingredients have not yet been regulated or fully disclosed to the public and have been known to cause allergic reactions which in some cases can be severe even well after the time of tattooing, or after exposure to sunlight or laser treatments. Despite the fact that there is a paucity of data in the literature concerning the toxicity and carcinogenicity of tissue markings as well as their long their long term effects on the body, they continue to be used today.
Statistics have shown that a large portion of people who have tattoos wish to have them removed. Since tattoos are generally designed to be permanent, their removal is very difficult. Overtattooing, dermabrasion, and surgical excision are typical “removal” methods as well as the more current method of using pulsed lasers. In laser removal; intense pulses of laser energy are specifically absorbed by the tissue marking particles. However, such methods require lasers emitting visible radiation, which consequently, depending upon the tattoo particle color and hence the wavelength of the laser radiation used, will result in absorption of the radiation by the skin and surrounding tissue, and thus cause collateral damage.
Such methods of tattoo removal can be categorized as “tattoo removal by dispersal” since the laser causes the pigment particles to break into minute particles for dispersal by the body's biological processes such as lymphatic transport system and/or immune processes. Using laser techniques to remove tattoos that utilize current tissue marking compositions have a number of disadvantages. Because of the reliance on “tattoo removal by dispersion”, the body is not only exposed to additional health hazards but also multiple treatments are required which are not only expensive but can be painful. Additionally, multiple lasers are needed for multicolored tattoos, while some pigments such as green and yellow are virtually impossible to remove.
U.S. Pat. No. 6,013,122 discloses removable tissue markings wherein pigment or dye particles are immobilized by a vehicle which surrounds such dye or pigment, that is, the colored particles are encapsulated in said vehicle and implanted into the skin. The vehicle, encasing the dye or pigment, ruptures when exposed to specific forms of energy, such as UV light or infrared energy and the pigment or dye is dispersed or dissipated (“tattoo removal by dispersal”) from the location in which it was administered, therefore erasing the tattoo image. It should be noted that tattoo removal by dispersal necessitates the colored particles to be small so that they can be dispersed to erase the tissue marking, which in turn requires the colored particles to be encapsulated, for otherwise, the tissue marking would not be permanent. As stated above “tattoo removal by dispersal” of the colored particles is inherently risky, as the body could be subjected to allergic or toxic reactions. If the colored compound is chosen to be biocompatible, then the choice of suitable dues will be significantly narrowed. Thus, the requirement of biocompatibility will significantly narrow the choice of suitable dyes. It should be noted that the above invention does not envision tattoo removal by rendering the dye or pigment colorless.
U.S. Pat. No. 6,814,760 provides for microparticles that create permanent tissue markings, such as tattoos, designed in advance for change and/or removal on demand, as well as methods for implanting the microparticles in tissue and methods to change and/or remove the implanted markings. The microparticles contain chromophores (colored particles) which are encapsulated by coating materials by a variety of encapsulation techniques such as aerosol collision, chamber deposition etc.
Two embodiments for the removable tissue marking compositions, which are in the form of microparticles, are envisioned. In the first embodiment, microparticles which contain chromophores (colored compound particles) are constructed such that tattoo removal is accomplished by dispersal of the colored compound particles, that is, the dispersal is achieved by making the microparticles permeable, such as by rupture of the coating comprising the microparticle. The chromophore (colored particles) is dispersed either by dissolution in bodily fluids, or by biological processes such as metabolism, lymphatic transport etc. It should be noted that tattoo removal by dispersal necessitates the colored particles to be small so they can be dispersed to erase the tissue marking which in turn requires the colored particles to be encapsulated, for otherwise, the tissue marking would not be permanent. Relying on dispersion as the removal technique exposes the subjects to health hazards by virtue of some of the tattoo particles entering the body such as in the lymphatic system.
In the second embodiment, microparticles can contain chromophores that are rendered invisible in-situ, that is, without rupturing the microparticles, and the chromophore does not need to be dissolved, metabolized or dispersed for removal of the marking. Thus the tissue markings can become invisible without the need for being released into the bodily fluids. This embodiment generally requires that the colored compound be selected such that it can absorb the triggering electromagnetic radiation. Lasers used to deliver the energy for tattoo removal for these bleachable chromophores would either be near UV, visible, or near infra red.
For the case wherein the tissue marking is rendered colorless with near UV energy, apart from health hazards to the subjects being exposed to such UV energy, the chromophores of such tissue markings will generally be subject to photolytic degradation, and hence, such tissue markings will be vulnerable to fading by prolonged exposure to sunlight, adversely affecting their permanence until the desire for removal.
Use of tissue markings that can be tendered colorless or bleachable by visible lasers will be similar to the current practice of tattoo removal, requiring multiple visits and, additionally, will not be devoid of tissue scarring or injury. Intense visible light can target the skin's natural pigment, melanin, resulting in temporary or permanent hypopigmentation or hyperpigmentation, especially in dark or tanned skin, and/or hair loss in the area.
The near infra red bleachable tissue markings will generally have colors in the red portion of the visible spectrum thereby severely limiting the color choices for the tissue markings.
Embodiments wherein the tissue marking is rendered colorless without rupturing the microcapsule, and not requiring the chromophore of the tissue marking to absorb the triggering radiation, that is, requiring the colored compound to contain a specific radiation absorbing component, is one wherein heat is used to release a second reactive component such as a strong acid, or strong oxidizing agent, or a thermal initiator generating free radicals which then must first come into contact with the pigment or dye and then react with it to bleach the chromophore. One can question the practice of introducing strong oxidizing/reducing agents or free radicals in the human body. Even though such materials may be encapsulated, they would pose significant health hazards since there is always a danger of leakage from the capsule. Further, such embodiments can result in fairly complex microcapsule constructions.
Thus there is a need for new, on-demand removable tissue marking compositions and methods for their use that are simple, that do not require use of hazardous materials for accomplishing the color removal, that do not require dispersal of the tissue marking for removing the marking, that is, markings wherein the color can be switched off in-situ, that embody methods of color change which do not adversely impact tattoo permanence, that minimize or eliminate the damage to the skin and surrounding tissue, and wherein the tattoo removal method would be applicable to a wide variety of colored materials.